First of all, thanks very much for the great pictorial. Can I ask a total Saiga noob question? I understand why you take the FSB off so you can put a standard threaded one on, but why do you have to take the gas block off? Will a standard ak gas tube not fit on the saiga GB? If so, is this true for all calibers? Thanks.

Gas tube length is the same. You would switch the gas block out if you wanted one with a lug on the bottom.